Under ordinary circumstances, the thermal regulatory system of the human body maintains a near constant temperature of about 37° C. (98.6° F.). This temperature is termed normothermia. Normothermia is generally optimum for efficient function of a healthy human.
The human body maintains normothermia through a number of very precise mechanisms that function to cool the body if it warms to far above normothermia, or to warm the body if it is becoming too cool. Normal cooling mechanisms may include, for example, dilation of the capillary beds exposed to the elements to enhance loss of heat from the body (peripheral vasodilatation), and sweating to create evaporative heat loss which, especially in combination with peripheral vasodilatation, can result in significant heat loss. If the body becomes too cool, on the other hand, the body has mechanisms that maintain warmth for the critical functions and to protect vital organs that include sequestering blood in the body's core to protect the vital organs, for example by AV shunting and capillary constriction in capillary beds exposed to the environment. Additionally, the body may shiver to produce additional metabolic heat.